Download OXOVANADIUM(IV) COMPLEXES WITH LIGANDS DERIVED BY

Acta Metallomica – MEEMB, 2014, Tome XI, Nos. 2-4, 171-179
OXOVANADIUM(IV) COMPLEXES WITH LIGANDS
DERIVED BY CONDENSATION OF 1,2-DIACETYLBENZENE
WITH 2-AMINOBENZAMIDE AND β-DIKETONES
Vijai SINGH, Probin BORA and Hardeo Singh YADAV*
Department of Chemistry, North Eastern Regional Institute of Science and Technology,
Nirjuli-791109, Itanagar, Arunachal Pradesh, India
*E-mail: [email protected]
The synthesis of a new parent oxovanadium(IV) complex, [VO(L)]SO4, is achieved
under in-situ experimental conditions where vanadyl ion acts as a kinetic template for
the ligand derived by condensation of 1,2-diacetylbenzene with 2-aminobenzamide in
1:2 molar ratio in aqueous ethanol medium. The parent complex, [VO(L)]SO4, has
reacted with β-diketones to get macrocyclic complexes of the general formula,
[VO(mac)]SO4, where mac = macrocyclic ligands derived by reactions of [VO(L)]SO4
with acetylacetone, benzoylacetone, thenoyltrifluoroacetone and dibenzoylmethane.
These vanadyl complexes are characterized and their tentative structures are
ascertained on the basis of elemental analyses, molar conductance, magnetic moments
and spectral data of electronic, infra-red and X-band electron spin resonance
spectroscopy. All the vanadyl complexes are five-coordinate with tetradentate chelating
ligands. These vanadyl complexes were screened for their antifungal activities against
Aspergillus niger and Aspergillus flavus, which showed promising antifungal activities.
Key words: vanadyl ion, macrocyclic complexes, 1,2-diacetylbenzene, β-diketones.
INTRODUCTION
The coordination chemistry of vanadium (Yuan et al., 2009; Rehder et al.,
2003) and particularly its biological (Baran et al., 2008; Guiotoku et al., 2007) and
catalytic activities (Selbin et al., 1966) have attracted huge interest in the synthesis
of oxovanadium(IV) complexes with a variety of ligands with nitrogen and oxygen
donor atoms. Recognition of vanadium in enzymatic systems such as in the
haloperoxidases (Brink et al., 2001) found in marine fungi and algae (Meisch et. al.,
1979) and in mushrooms (Adetutu et al., 2010); have induced enhanced curiosity to
study vanadium role in biological systems and catalytic areas. Reports are available
for vanadyl complexes in its +4 and +5 oxidation states showing insulin like
activities (Shukla et. al., 2008), anticancer, antitumor, antibacterial and antifungal
activities (Pasayat et al., 2012; Dash et al., 2012). The vanadyl complexes are
reported to influence many enzymatic systems such as phosphatases, ATPases,
peroxidases, ribonucleases, protein kinases and oxidoreductases (Wilkinson et al.,
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Vijai Singh et al.
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1987). There are reports that vanadium enters into the organism by inhalation, the
gastrointestinal tract and the skin, which is specifically stored in certain organs
mainly in the liver, Kidney and bones (Cusi et al., 2001). In order to explore the
pharmaceutical applications of vanadyl ion in complexed form, a series of
oxovanadium(IV) complexes with ligands derived by condensation of 1,2diacetylbenzene with 2-aminobenzamide in 1:2 molar ratio in aqueous ethanol
medium and their cyclisation with β-diketones is reported, where vanadyl ion play
a key role as kinetic template. The antifungal studies of these vanadyl complexes
are carried out against Aspergillus niger and Aspergillus flavus.
MATERIALS AND METHODS
Materials
Reagent grade chemicals and solvents were used in the synthesis. Vanadyl
sulphate, 1,2-Diacetylbenzene and 2-Aminobenzamide used were Aldrich products.
The β-diketones such as acetylacetone, benzoylacetone, thenoyltrifluoroacetone
and dibenzoylmethane were Sisco Research Laboratory products.
Analytical and physical measurements
Standard gravimetric method was used for quantitative estimation of
Vanadium as its sodium vanadate (Vogel et al., 1978). Estimation of Sulphur was
made as barium sulphate (Vogel et al., 1978). The standard method for
determination of melting point (uncorrected) was employed using sulphuric acid
bath. Toshniwal conductivity bridge, model no. CLO102A was used for
conductance measurements at room temperature. The magnetic susceptibility of the
complexes in powder form was carried out at room temperature using Guoy’s
balance. Mercury tetrathiocyanatocobaltate(II), Hg[Co(CNS)4], (Xg = 1644 x 10-6
c.g.s. unit at 200 C) was used as calibrant. The electronic spectra of the complexes
were recorded on Beckmann DU-2 spectrophotometer in the ranges 2000 – 185 nm
using dimethylformamide as solvent. The room temperature and liquid nitrogen
temperature E.S.R. spectra were recorded at SAIF, IIT Mumbai, India. The infrared
spectra of the complexes were measured on IRAffinity-1, FTIR spectrophotometer,
SHIMADZU using KBr pellets in the range 4000 cm-1 – 200 cm-1.
In-situ preparation of oxovanadium(IV) complex with ligand derived by condensation of
1,2-diacetylbenzene with 2-aminobenzamide ( 1:2 )
Vanadyl sulphate (2 mmol) was dissolved in methanol (25 mL), which was
added into a refluxing solution of 1, 2-diacetylbenzene (2 mmol) and
2-aminobenzamide (4 mmol) in ethanol (25 mL). The reflux of the reaction mixture
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Oxovanadium (IV) complexes
173
was continued for 5 hours, when the color of the solution turned green with little
precipitation. A dark green color product was isolated after evaporating solvent
under vacuum. The isolated complex was thoroughly washed with methanol /
ethanol (1:1) mixture (10 mL). The yield was found to be 70%.
In-situ preparation of macrocyclic complexes of oxovanadium(IV) using β-diketones as
ring closing reagents
Vanadyl sulphate (2 mmol) was dissolved in methanol (25 mL), which was
added into a refluxing solution of 1, 2-diacetylbenzene (2 mmol) and 2aminobenzamide (4 mmol) in ethanol (25 mL). The reflux of reaction mixture was
continued for 5 hours, when the color of the solution turned green with little
precipitation. To this reaction mixture, an ethanolic solution (10 mL) of
acetylacetone (2 mmol) and glacial acetic acid (1 mL) were added. This reaction
mixture was refluxed further for about 3 hours and a green precipitate was isolated
after cooling the solution. The vanadyl complex was purified by washing with a
methanol / ethanol (1:1) mixture (10 mL). The yield was found to be 60%. A
similar procedure was followed for the synthesis of other oxovanadium(IV)
macrocyclic complexes using benzoylacetone, thenoyltrifluoroacetone and
dibenzoylmethane.
RESULTS AND DISCUSSION
The physical and analytical data of the complexes are presented in Table 1
and the reaction scheme is presented in Scheme1.
Scheme 1
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Vijai Singh et al.
As shown in the reaction scheme 1, the parent oxovanadium(IV) complex
was synthesized by in-situ method by refluxing the reaction mixture containing
vanadyl sulphate, 1,2-diacetylbenzene and 2-aminobenzamide in 1:1:2 molar ratios
in aqueous ethanol medium. The reaction appears to proceed as follows:
(VOSO4).3H2O + 1, 2-Diacetylbenzene + 2-Aminobenzamide → [VO(L)]SO4 + 5 H2O
Scheme 2
The oxovanadium(IV) complex was reacted with β-diketones in 1:1 molar
ratio, which resulted formation of macrocyclic complexes, [VO(mac)]SO4, by
condensation of the terminal amino group with ketonic group of β-diketones. The
elemental analyses of the oxovanadium(IV) complexes show a 1:1 metal to ligand
stoichiometry.
Table 1
Physical and analytical data of the oxovanadium(IV) complexes
Complex
Formula
number
C22H22N4O7VS
[VO(L)]SO4
Decompositi
on
temperature
(0C)
260
C29H26N4O7VS [VO(mac1)]SO4
264
C34H28N4O7VS [VO(mac2)]SO4
265
C32H23N4O7VSF VO(mac3)]SO4
264
C39H30N4O7VS VO(mac1)]SO4
265
C (%) H (%) N (%) V (%) S (%)
Found Found Found Found Found
Calcd. Calcd. Calcd. Calcd. Calcd.
51.28
51.34
55.65
55.68
59.34
59.39
51.35
51.40
62.46
62.48
3. 90
3.92
4.13
4.16
4.00
4.07
3.02
3.07
3.98
4.00
9.96
9.98
8.93
8.96
8.12
8.15
7.46
7.49
7.45
7.47
9.00
9.08
8.14
8.15
7.39
7.41
6.78
6.81
6.78
6.80
5.68
5.70
5.10
5.12
4.61
4.65
8.52
8.56
4.24
4.27
µeff. BM
300K
1.71
1.73
1.72
1.73
1.72
Where L = Ligand derived by condensation of 1, 2-Diacetylbenzene with 2-Aminobenzamide (1:2)
mac1 = Macrocyclic ligands obtained by reaction of L with Acetylacetone.
Mac2 = Macrocyclic ligands obtained by reaction of L with Benzoylacetone.
Mac3 = Macrocyclic ligands obtained by reaction of L with Thenoyltrifluoroacetone.
Mac4 = Macrocyclic ligands obtained by reaction of L with Dibenzoylmethane.
INFRARED SPECTRA
The most relevant characteristic infrared bands of the oxovanadium(IV)
complexes are listed below:
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Oxovanadium (IV) complexes
Table 2
Characteristic infrared spectral bands (cm-1) of the oxovanadium(IV) complexes
Complex
v(CN)+ SO42- SO42 SO42 (N-H) (N-H)
∂(NH)
(Amide-) (Amide-II) v3
v1
v4
vasym vsym
v(>C=N) v (V-N) v(V=O) v(C=O)
[VO(L)]SO4
1610
304
980
1665
1650
1135
956
600
[VO(mac1)]
SO4
[VO(mac2)]
SO4
[VO(mac3)]
SO4
[VO(mac4)]
SO4
1605
302
981
1662
1648
1134
954
602
1605
304
982
1664
1650
1132
956
604
1610
302
981
1664
1648
1135
954
604
1605
301
980
1662
1648
1134
956
602
3352
3170
The IR spectrum of the [VO(L)]SO4 complex shows bands at 1610 cm-1,
which may be assigned to the coordinated azomethine group (Sreeja et. al., 2005;
Yadava et. al., 1987). The infrared bands appearing at 1665 cm-1 and 1650 cm-1 are
assigned to the coordinated amide-I, v (C=O) and amide-II, v(CN) + ∂ NH
(Maurya et al., 2006). The bands appearing at 3352 cm-1 and 3170 cm-1 may be
assigned to asymmetrical and symmetrical N-H stretching modes of the noncoordinated terminal amino groups of the ligand, L (Nonoyama et al., 1975).
A band at 304 cm-1 further supports the coordination of nitrogen atom to vanadium,
as it may be assigned to v (V-N) vibrations (Sakata et al., 1989). The presence of
an intense band at 980 cm-1 may be assigned to v (V=O) vibration (Samanta et al.,
2003). The ionic sulfate group in the complex is indicated (Tsuchimoto et al., 2000) by
three bands at 1135 cm-1 (v3), 956 cm-1 (v1) and 600 cm-1 (v4). The absence of v2
band and non-splitting of v3 band indicate that Td symmetry is retained. The
infrared spectra of the other macrocyclic oxovanadium(IV) complexes as detailed
in Table 2 have similar patterns except that vasym. and vsym. vibrations of the
terminal -NH2 group disappear after the ring closing reaction with β-diketones and
infrared bands of uncoordinated v(>C=N) appear.
MAGNETIC MOMENT AND ELECTRONIC SPECTRA
The magnetic moment values of all the oxovanadium(IV) complexes were
found in the range 1.71 – 1.73 B.M. at room temperature, which are well within the
range reported for vanadyl complexes with paramagnetic center (Sarkar et al.,
2008). This data confirm the mononuclear nature of oxovanadium(IV) complexes.
The electronic spectra show bands in the regions 11,130 – 11,900 cm-1, 15,200 –
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Vijai Singh et al.
15,900 cm-1, which are in accordance other reports for oxovanadium(IV) complexes
involving nitrogen/oxygen donor atoms. According to Ballhausen and Gray
scheme, these electronic bands have been assigned to 2B2 → 2E, 2B2 → 2B1 and
2
B2 → 2A1 transitions respectively. One more electronic band observed in the
region 35,200 – 35,700 cm-1 may be assigned to the transition arising out of
azomethine linkages.
ESR SPECTRA
The X-band ESR spectra of the oxovanadium(IV) complexes were recorded
at room temperature and liquid nitrogen temperature, which show eight lines due to
hyperfine splitting originating basically from the interaction of unpaired electron
with a 51V nucleus having the nuclear spin no. I = 7/2 (Mishra et. al., 2005; Ando
et. al., 2003). Anisotropy is not evidenced at room temperature because of rapid
tumbling of molecules in solution and only g-average values are obtained.
2800
3000
3200
3400
3600
3800
(G)
Fig. 1. X-Band ESR spectrum of [VO(L)]SO4 at liquid nitrogen temperature (77 K).
However, as observed in Fig. 1, an isotropy is clearly visible in the spectra at
liquid nitrogen temperature and eight lines each due to gıı and g┴ are observed
separately showing gıı < g┴ and Aıı > A┴. The gıı, g┴, Aıı and A┴ values, which are
measured from the ESR spectra, are in good agreement for square pyramidal
structure.
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Oxovanadium (IV) complexes
Table 3
X Band ESR spectral data of oxovanadium(IV) complexes
Complex
[VO(L)]SO4
[VO(mac1)]SO4
[VO(mac2)]SO4
[VO(mac3)]SO4
[VO(mac4)]SO4
Room
Temp.
ıg ı
1.980
1.98
1.981
1.982
1.982
Liquid nitrogen temperature
gıı
1.930
1.932
1.931
1.932
1.931
g┴
1.970
1.973
1.972
1.973
1.972
ıgı
1.956
1.959
1.958
1.959
1.958
Aıı
190.70
190.80
190.60
190.72
190.71
A┴.
66.48
65.90
65.88
65.90
65.92
ıAı
107.88
107.53
107.45
107.50
107.51
ANTIFUNGAL ACTIVITY
The oxovanadium(IV) complexes were tested for their antifungal activity
against the fungi Aspergillus flavus and Aspergillus niger using standard methods
(Rehman et al., 2013). All tested complexes showed significant antifungal activity
but [VO(mac3)]SO4 was found to be the most active, which may be due to sulphur
and fluorine atoms present in the thenoyltrifluoroacetone, a cyclising agent as
β-diketone. The Fluconazole (75 µg/mL) was used as a standard drug. The stock
solutions of the oxovanadium(IV) complexes (100 µg/mL) were prepared in
dimethylformamide (DMF), and were added to potato dextrose sugar (PDA). This
mixture was poured into sterile Petri dishes and allowed to solidify. Fungal spores
were inoculated at the center of the medium. Finally, the Petri dishes were incubated at
303 K for 72 hours. The percentage inhibition was calculated by the equation:
% Inhibition = (C-T) x 100 / C
Where C is the diameter of the fungal colony in control plate and T is
diameter of fungal colony in test plate. The antifungal activity of the oxovanadium(IV)
complexes are summarised below in Table 4.
Table 4
The antifungal activity of the oxovanadium(IV) complexes
Zone of inhibition (in)*
Aspergillus
Aspergillus niger
flavus
[VO(L)]SO4
64
68
[VO(mac1)]SO4
63
69
[VO(mac2)]SO4
66
68
[VO(mac3)]SO4
76
80
[VO(mac4)]SO4
67
69
**
Fluconazole
100
100
**
Standard Drug, * average of three replicates
Complex
Conc. (µg/mL)
100
100
100
100
100
75
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Vijai Singh et al.
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The antifungal activities of oxovanadium(IV) complexes are attributed to the
reduced polarity of metal ion after coordination by ligand molecule, which could
enhance the lipophilic character of the central metal ion increasing its permeability
through the lipid layer of the cell membrane. This significantly enhances the
antifungal property of VO(IV) complexes.
CONCLUSIONS
1,2-Diacetylbenzene has been used as precursor molecule having two
reactive carbonyl groups capable of undergoing Schiff base condensation with 2aminobenzamide in 1:2 molar ratio in aqueous ethanol medium. The parent
complex, [VO(L)]SO4 has been reacted with β-diketones to get macrocyclic
complexes of the general formula, [VO(mac)]SO4, where mac=macrocyclic ligands
derived by reactions of [VO(L)]SO4 with acetylacetone, benzoylacetone,
thenoyltrifluoroacetone and dibenzoylmethane, which are thoroughly characterized.
The oxovanadium(IV) complexes were tested for their antifungal activity against
the fungi Aspergillus flavus and Aspergillus niger, which showed significant
antifungal activity especially in the case of [VO(mac3)]SO4 (76 % and 80 %,
respectively). This may be due to sulphur and fluorine atoms present in the
thenoyltrifluoroacetone, a β-diketone used as a chelating agent.
Acknowledgements: The authors are thankful to the Director, NERIST, Nirjuli, Itanagar, Arunachal
Preadeh, India for extending laboratory facilities and spectroscopic support to complete this research
work by Central Research Facility, NERIST, Nirjuli-791109, Itanagar, Arunachal Pradesh, India.
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